The present invention generally relates to punch presses. More specifically, the present invention relates to a punch press having a positioning system for shifting of one or more clamps and/or a workpiece being held by the clamps in the x-axis and/or the y-axis.
In punch presses, work clamps which hold workpieces in a particular location are typically shifted in both the x-direction and the y-direction so as to position the workpiece in a particular location to enable punching or the like thereof. The positioning of the workpieces and the tools for punching the same may take place manually or automatically, such as by computer control.
A standard type of computer controlled automatic punch press is known, such as a computer-controlled turret press. Such a press is equipped with a vertically moving ram centered at a work station. A pair of spaced-apart rotatable turrets are provided with a plurality of circumferentially spaced tool holding sections. The upper turret carries a plurality of different punches, and the lower turret carries a plurality of corresponding dies shaped to mate with the punches. The turrets rotate in unison presenting a selected pair of a punch and a die to the work station. The workpiece is insertable into the space between the turrets such that, upon activation of the ram, a selected punch at the work station can be forced through the workpiece and into the die.
Movement control of the workpiece is typically performed by a coordinate movement mechanism associated with a workpiece supporting table. Standard movement systems include a carriage assembly moveable towards and away from the work station. The carriage assembly is typically equipped with two or more clamps which moves in unison transverse to the direction of the work station.
In modern punch presses, each of the clamps may be independently repositionable along the length of the carriage so as to accommodate different size workpieces. More recently, automatic repositioning of workpiece clamps has been provided wherein each of the clamps can be disengaged from its fixed position on the carriage and automatically moved to a different position, all under the control of a central processor unit.
In order to provide maximum exposure of the workpiece to the work station, such clamps are generally constructed as "pass-through" clamps having a vertical height which is less than the spacing between the turrets. Because of this, it is possible for the clamp, or the tip of the clamp, to be positioned at the work station where activation of the ram would cause serious damage to the clamp, the punch or the machine itself.
To prevent this, work clamps are commonly provided with projecting wire guards which can signal the controller when the clamp is in a danger zone thereby inhibiting operation of the ram. Such projecting guards, however, prevent the clamp from positioning the portion of the workpiece immediately adjacent the clamp to the work station and thereby reduce the area of the workpiece that can be acted upon by the punch without repositioning of the work clamp. Furthermore, the wire guards may reduce the speed at which the clamps may move.
While it is also further generally known to program the position of the work clamp into the movement control system such that the control system "knows" where the clamp is, a large safety margin must be provided in the control system since the accuracy of the knowledge of the positioning of the work clamp may not be precise and further since the geometry of the tool, i.e., the punch, changes. Commonly used punches may vary from a small diameter punch on the order of, for example, one-eighth of an inch to very large punches or notching units which may, for example, be as large as four or six inches in diameter.
Therefore, in order to provide a safe no-punch zone, i.e. that position of the workpiece movement device in which punching will not be permitted in order to protect the clamp, it is necessary to know the exact position of the clamp along the length of the carriage, the exact position of the carriage with respect to the work station, the calculated position of the clamp with respect to the work station calculated from the location of the clamp along the carriage and the position of the carriage, the geometry of the clamp and the geometry of the tool. In addition, a safety factor may be desired corresponding to an additional error factor which may exist in the carriage control and the possible off-centering of the punch with respect to the work station.
When all these factors are known and calculated, a minimal no-punch zone can be determined. Once, however, a determination has been made, it must be recognized that since the clamps are repositionable, the determination of clamp position must be re-input to the controller both upon the initiation of each reactivation of the machine and upon the occurrence of any automated or manual movement of the clamps.
Therefore, a need exists for an improved system for determining the position of the clamps in relation to the tools included in a tool holder, such as a turret, for example, of a punch press.